Electromagnet and control therefor



May 1, 1923. 1,453,555

G. E. STACK ELECTROMAGNET AND CONTROL THEREFOR Filed Dec. 21, 1920 WV WY Law /6' l7 6 A9 A7 Inventor: George Eiitamk, Joy. fiwm H is Attorn ey Patented May 1 19239 UNlTEl) GEORGE E. STACK, 0h BALLSTODT SPA, NEW YGRK, ASSXGNOR T0 GENERAL ELECTRIC (302:1?ANY, A CQR'LORATION OF NEW YQRK.

ELECTROIMIAGNET AND CUTHTBSOL Application filed December 21, 1920. Serial lie. 432,331.

To all whom it may concern:

Be it known that I, Gnoson E. STACK, a citizen of the United States, residing at Ballston Spa, in the county of Saratoga, State of New York, have invented certain new and useful Improvements in Electromagnets and Control There-for, of which the following is a specification.

My invention relates to improvements in electromagnets and the control of the same, and in particular to improved means for antomatically reducing the current in the magnet winding when the movable element of the electromagnet has reached the full limit of its stroke.

My invention has a particular application in the control of electromagnetic switches, although it is not necessarily limited thereto, since it is applicable generally to the control of electromagnetic devices. T he energy required to maintain the movable element of an electromagnet in its attracted position is considerably less than the energy required to attract the movable element to its operated osition. The large amount of current initially required to operate the electromagnet is apt to cause overheating of its coil if continued. A well known arrangement for re- (lucing the current in the coil circuit of the electromagnet after it has responded, is that of an auxiliary switch connected in any suitable manner to the movable element of the electromagnet so that the final movement of the movable element operates the auxiliary switch and introduces a resistance in the circuit of the magnet coil.- Pouch an arrangement has the disadvantage that the auxiliary switch must be operated before the movable element of the electromagnet has completed its stroke, and the movable element is liable to be either not attracted to the full extent of its movement or else will finally complete its movement alter objectionable vibrating or telegraphing thereof. This vibrating or telegraphing is due to the premature reduction of the tion by the insertion of the protective resistance.

One of the objects of my invention is to insure that the current in the electromag'net coil will be reduced after the movable element of the electromagnet has completed its movement but not before. In carrying my magnetic attracinvention into effect, 1 take advantage of the fact that when the electromagnet coil is first connected to the supply circuit there is a substantially definite rate of change of the magnetic flux in the magnet structure, and 1 cause a protective resistance to be inserted in series with the electromagnet coil responsively to the rate of change of the magnetism in the magnet structure of the electroniagnet. 'At the instant the electromagnet is connected to a source of supply the rate of change of the magnetization of the electromagnet is comparatively great, but after the movable element of "the elec'tromagnet has completed its n'iovement the magnetization will become substantially constant after a brief interval. In carrying my invention into effect in one form, I provide a coil on the magnetic structure of the electromagne't which is inductively related to the main coil and which acts as the secondary of a transformer (the main coil of the electromagnet acting as the primary) and energizes an auxiliary switch which controls a resistance in the main coil circuit. The potential applied to the coil of the auxiliary switch will be sullicient to cause the auxiliary switch to close its contacts and short-circuit the resistance in series with the main or operating coil of the electromagnet to be controlled when the operating coil is connected to a source of supply. but when the electromagnet has operated and the magnetization of its magnet structure becomes substantially constant, the potential applied to the coil of the auxiliary switch will be reduced to a negligible value. The auxiliary switch will thereupon be permitted to open and insert the resistance in series with the electromagnet coil alter the electromagnet has operated.

For a better understanding of my invention, reference is had to the accompanying drawings wherein l have, illustrated one form of my invention as applied to the control of an electromagnetic switch for purposes of illustration, and in which the main electromagnetic switch is provided with a movable switch member 10, and an operating electromagnet comprising an operating coil 11 properly disposed on the magnet structure 12 or the switch. A resistor 13 is provided 'for reducing the current in the coil 11 after the switch member 10 has completed its movement to the attracted position, that in which the load is connected to the source of supply 14. This resistor 13 is controlled by means of an auxiliary electromagnetic switch having a movable switch member 15 and an operating electroinagnet comprising a coil 16 suitably disposed upon a magnet structure 17. The coil 16 receives its energy from the auxiliary coil 18 disposed on the magnet structure of th main switch in such a way that the main coil 11 serves as the primary of a transformer and the auxiliary coil 18 serves as the secondary of the transformer.

The operation of my invention as thus constructed and arranged is as follows:

lVith the parts in the various positions shown in the drawing, the closing of the pilot switch 19 connects the coil 11 ot' the main. switch to the source of supply let momentarily through the resistor 13. By reason of the inductive effect, the current in the main coil 11 will not be instantly established at the full value, but will increase at an approximately definite rate. The auxiliary coil 18 is disposed on the magnetic circuit 12 in such a way that it serves as the secondary of a transformer, and the voltage induced in this auxiliar coil will be responsive to the rate of cliange of the magnetism in the magnetic structure. There fore, an instant after the closing oithe pilot switch 19, the coil 16 on the auxiliary switch which controls the resistor 13 will be energized to such an extent that the switch member 15 will be attracted and short-circuit the resistor 13, thereby permitting full potential to be applied to the main coil 11. The Shortcircuiting of the resistor 13 produces a further change in the magnetization of the magnetic structure of the main switch, the winding 16 of he auxiliary switch will be maintained energized temporarily to short-circuit the resistor. its the movable switch member 10 moves towards its attracted position, tl at in which the load is connected to the source oi supply, the magnetization of the magnetic structure of the main switch v ialso correspondingly change, thereby inducin a potential in the secondary coil 18 which will energize the auxiliary switch to maintain the resistor 13 temporarily short-circuited. The resistor 13 will be maintained short-circuited until after the switch member 10 of the main switch has completed its movement to the attracted position, but after the switch member 10 has closed, the rate of change in the magnetic structure of the main switch will decrease to approximately zero. Since the auxiliary switch which controls the resistor 13 is energized responsively to the rate of change of the magnetism in the main switch, when the magnetism in the main switch becomes a substantially constant value, the winding 16 will be substantially deenergized, thereby permitting the switch member 15 to open and insert the resistor 13 in series with the main coil 11 of the main switch. The insertion of the resistor 13 will produce a change of the magnetism in the main switch, but this will be a minor change and the auxiliary switch will be designed so that it will not respond to this change. maintained in series with the switch winding 11 until the pilot switch 19 is opened.

My invention, in the form illustrated in the drawings, has a particular application to large electro-magnets in which the operating current in the coil winding is a considerable value, but it is not necessarily liniited to large electroinagnets but is adapted generally where it is desirable to reduce the current in the operating winding of an electromagnet after the electromagnet has operated to perform the work for which it is provided.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but

I desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by other means.

hat I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination with an electromagnet and a movable member operated in response to the energization of the magnet winding, of means operated responsively to the rate of change of the magnetism of the electroi'nagnet for automatically reducing the current in the magnet winding.

2. The combination with an electromagnct caving an operating winding and an auxr winding inductively related thereto, movable member operated in response e energization of the operating winding, and means operated responsively to the voltage induced in the auxiliary coil for automatically reducing the current in the operating winding.

The combination with an electromagnct O. and a movable member controlled. thereby, of a. resistor for reducing the current in the magnet winding, and means controlled responsively to the rate of change ,of the magnetism in the electromagnet for controlling the said resistor.

.1-. The combination with an electromagnetic switch having a movable switch member and an operating electromagnet therefor, of a resistor for reducing the current in the ma net winding, and means controlled responsively to the rate of change of the mag- The resistor 13 will be' netism in the operating electromagnet for introducing the resistor in the coil circuit of the operating electromagnet.

5. The combination with an operating electromagnet having a movable member controlled thereby, of a resistor for reducing the current in the magnet winding, and an auxiliary electromagnetic switch for controlling the said resistor, the said auxiliary switch having a winding energized in accordance with the rate of change of the magnetism in the operating electromagnet.

6. The combination with an electromagnetic switch having a movable switch member and an operating electromagnet therefor having two coils, one of which is an operating coil and the other of which serves as asecondary of a transformer of which the operating coil is the primary, a resistor for reducing the current in the operating coil, and an electromagnetic switch energized from the said secondary coil for controlling the resistor.

7. The combination with can electromagnet having a movable member operated in response to the energization of the magnet winding, of a resistor normally in the circuit of the magnetwind-ing, and means operated responsively to the rate of change of the'current in the said winding for short circuiting the said resistor an interval after the winding is energized to operate the said member and then reinserting the resistor to reduce the current in the winding when the current in the winding becomes substantially I constant.

In witness whereof, I have hereunto set my hand this 20th day of-Dec., 1920.

GEORGE E. STACK. 

